Art of mounting piezoelectric elements



P. D. GERBER 2,264,692

ART OF MOUNTING PIEZOELECTRLC ELEMENTS Filed July 5l, 1940 Patented Dec. 2, 1941 TES PATENT OFFICE ART OF MOUNTING PIEZOELECTRIC ELEMENTS Paul D. Gerber, Woodlynne, N. J., assigner to Radio Corporation of America, a corporation of Delaware 10 Claims.

This invention relates to the art of mounting piezoelectric elements and has special reference to improvements in methods and means for mounting quartz elements of the type that exhibits a shear-mode of vibration. Thus, it will be understood that the invention herein described is applicable to all quartz resonators and oscillators except so-called X-cut crystals which, as is well known to those skilled in the art, exhibit a longitudinal type of vibration.

The principal object of the present invention is to provide an improved mount for shear-mode crystals and wherein the necessary clamping or other mounting force is applied to the crystal in a manner which results in the minimum sacrifice in amplitude and constancy of vibration.

Other objects and advantages, together with certain preferred details of construction will be apparent and the invention itself will `be best understood by reference to the following specification and to the accompanying drawing wherein Figure 1 is a top plan view of a pressure airgap mounting embodying the invention,

Figure 2 is a sectional view taken on the line 2--2 of Fig. 1,

Figures 3, 4 and 5 are sectional views showing other crystal mounting arrangements within the invention,

Figures 6 and 7 are views in perspective of still other crystal assemblies embodying the invention.

It can -be demonstrated that a quartz piezoelectric element of the type that exhibits a shearmode of vibration has its zone of minimum oscillatory movement in a plane which is centered through all of the minor surfaces of the elemenlt. It has previously been recognized that in installations requiring the use of a clamping force it is usually advantageous to apply such force along a nodal plane or along a nodal axis of the crystal element. In an effort to apply this teaching of the prior art to crystals of the shear-type, it has previously been proposed to bevel the sides of the crystal element to a knife edge and to apply the clamping force inwardly in the direction along the said knife edges. Obviously, when the crystal is operated in such a mounting it may become fractured or chipped adjacent its thin edges. f perhaps more importance is the fact that the clamping force in such a mount is applied to the crystal in the direction or directions in which it vibrates, and the oscillations may, for this reason, be damped to an undesired degree.

The foregoing and other disadvantages inherent in known methods of mounting shear-mode crystals are substantially obviated in accordance with the present invention by applying the mounting force to the crystal element adjacent and in a direction normal to its plane of minimum oscillatory movement. To this end, referring now to the drawing (wherein like reference characters designate the same or corresponding parts in all figures), the opposite electrode faces F, F' of the crystal C, or one of them, is provided with one or more cut-away portions or detents D, which extend into the crystal to a point adjacent its plane P-P of minimum movement, and the clamping, gravitational, or other mounting force is applied to the base of the cutaway portion or portions, i. e., in a direction normal to the plane (P-P) of minimum oscillatory movement.

In Figs. l and 2, the invention is shown as applied to a so-called pressura air-gap type of mounting. In this case, the crystal 2C is supported above a bottom electrode plate 2E on insulating grommets 2G which extend into the detents 2D in the adjacent electrode faces 2F of the crystal. The top electrode 2E is supported on insulating spacers 2R above the top electrode face 2F. A clamping force is applied to the crystal by means of screws 2S, the heads of which are received in the detents 2D, which are in register with the bottom detents 2D and are spaced inwardly away from the edges of the crystal.

In the pressure air-gap type of mounting shown in Fig. 3, the edges of the crystal 3C are cut away to provide a pair of oppositely located outwardly extending integral arms 3D, upon which the rims r of a pair of cup-shaped electrode 3E, 3E' are seated. The clamping force is applied adjacent the central plane of minimum movement as by means of screws 3S which extend through the rims of the electrodes 3E, 3E' and the arms 3D, 3D on the crystal.

Fig. 4 shows the invention as applied to an air-gap holder of the gravity type wherein the crystal 4C is supported without any clamping force upon an integral rim 4D, which is provided for the purpose, adjacent its opposite ends. The rim 4D may extend entirely around the crystal, if desired, and its base may, in any event, coincide with the plane P--P of minimum oscillatory movement.

In the embodiment of the invention shown in Fig. 5, the detents 5D, 5D in the crystal 5C are adjacent its center and the electrodes 5E, 5E are in the form of metallic lms applied directly to the opposite electrode faces of the crystal. A pair or electrode leads 5w are shown cemented to the crystal within the central detents, beneath but in contact with the iilm-like electrodes.

In Fig. 6, as in Fig. 5, the electrodes which are here designated 6E, 6E are in the form of metallic films applied directly to the electrode faces of the crystal 6C. In this case, however, the detents 6D within which the mounting force is applied are at the opposite corners of one end of the crystal and the mounting elements BS extend through the crystal. In order to obviate the possibility of a short circuit between the opposite electrodes 6E, 6E', the plating adjacent the diagonally opposite corners of the crystal may be erased, as indicated at 6e, 6e. The mounting elements SS which, as in the embodiments of the invention shown in Figs. 2, 3 and '7, may be in Ythe form of screws, are shown aiiixed to a supporting block 6B. Ordinarily, the crystal assembly of this embodiment of the invention will be mounted in a vertical position.

Fig. '7 shows another embodiment oi the invention wherein the crystal assembly may be mounted in a vertical position without sacrifice of rigidity. Here, as in Fig. 6, the detents 1D, 'ID' within which the clamping force is applied are at the opposite corners of one end of the crystal 1C. The electrodes, however, are in the form of separate plates 1E, 1E', and are maintained in spaced relation with respect to the electrode faces TF, 'IF' of the crystal by insulating grommets 'HG through which the clampingforce is applied to the crystal adjacent and in a direction normal to its plane P-P of minimum movement.

Various modications of the several embodiments of the invention herein described will suggest themselves to those skilled in the art. It is to be understood, therefore, that the foregoing is to be interpreted as illustrative and not in a limiting sense, except as required by the prior art and by the spirit of the appended claims.

What is claimed is:

1. Method of'mounting a quartz piezoelectric element of the type that exhibits a shear-mode of vibration, said method comprising applying a mounting force to said element adjacent and in a direction normal to its plane of minimum oscillatory movement.

2. Method in accordance with claim l and wherein the mounting force applied to said element comprises a clamping force.

3. Method in accordance with claim 1 and wherein said mounting force is gravitational in character.

4. In combination, a quartz piezoelectric element of the type that exhibits a shear-mode of vibration, and means for applying a mounting force to said element adjacent and in a direction normal to its plane of minimum oscillatory movel ment.

5. In combination, a quartz piezoelectric element of the type that exhibits a shear mode of vibration, and means for applying a clamping force to said crystal in opposite directions adjacent and in a direction normal to its plane of minimum oscillatory movement.

6. In combination, a quartz piezoelectric element of the type that exhibits a shear-mode of vibration, said element having a cut-away portion which extends in a direction substantially normal to its electrode faces to a point adjacent the plane of minimum oscillatory movement of said element, and means for mounting said element adjacent its said cut-away portion.

7. A quartz piezoelectric element of the type that exhibits a shear-mode of Vibration, said element having a cut-away portion which extends in a direction substantially normal to its electrode faces to a point adjacent its plane of minimum oscillatory movement.

8. The invention as set forth in claim 7 and wherein said cut-away portion lies adjacent the center of said quartz element.

9. The invention as set forth in claim 7 and wherein said cut-away portion is provided in each of the electrodefaces of said quartz element.

l0. The invention as, set forth in claim '7 and wherein said cut-away portion lies adjacent an edge of said quartz element.

PAUL D. GERBER. 

